1. Field of the Invention
The present invention provides a vertical and a horizontal vacuum sublimation apparatuses with high efficiency and processes, which can be applied to the mass production of high purity chemicals.
2. Description of the Related Art
With the development of IT and electrical industries, the requirements for the quality of electronic components are continuously rising. The purity of the chemicals used in electronic components is the main quality-affecting factor. Some chemicals cannot be purified via distillation process since their melting temperature is higher than their decomposition temperature. Sublimation purification is one of the processes for obtaining high purity chemicals. It can be applied to chemicals with high melting temperature and sublimation characteristics. It is based on these sublimation characteristics that purification can be realized via high vacuum heating sublimation process, where contaminants must be blocked off from the sublimation process. Products with extremely high purity can only be obtained under a strictly controlled operation environment to produce high quality electronic components. Some illumination layer materials are used in the production of OLED components, such as electron transport layer (ETL) materials: Aluminum Tri (8-Hydroxyquinolinate) (Alq3); hole injection layer (HIL) materials: Copper Phthalocyanine (CuPc); hole transport (HTL) layer materials: N,N′-bisphenyl-N,N′-bis(1-naphthyl)-benzidine (abbreviated as NPB), etc. The purification of these chemicals cannot be realized through distillation process since their melting temperature is higher than their decomposition temperature. However, high purity products can be obtained through vacuum sublimation process based on their sublimation characteristics to produce high quality electronic components.
Although the earlier approach of promoting sublimation vapor with noble gases could lower the requirements on the vacuum degree of the system, but the residual substances that cannot be sublimated in the sublimation materials have low apparent density, so they are easy to flow with noble gases, which causes the contamination of products by the flowing residues. High vacuum system is therefore designed to overcome the above disadvantages. In addition, the vapor pressure of some materials, such as CuPc, is extremely low, and a system with vacuum degree of 10−6 mbar temperature of 600° C. is required. Otherwise, these materials can not be evaporated. If the pressure of the system were too high, the vapor from the sublimation process would collide with the residual air in the system, causing the sublimated materials to fall back into the evaporation tank and creating partial vaporization-condensation circulation, thus resulting in difficulties for product output. Recently, with the continuously increasing demand for such high purity chemicals, materials produced by small-scale purification apparatuses can no longer meet the demand because of their uneven quality of each product group and limited productivity. As a result, it is necessary to design a vacuum sublimation apparatus that can be applied to mass production.
Instead of considering the purity of products and the convenient operational approaches required by mass production, the processes revealed by existing patent documents primarily are concerned with improving sublimation efficiency. In the manufacturing process of OLED materials, the purity of the materials is the key factor to a successful production. How to obtain high purity sublimated products from mass production is the main challenge of these apparatuses.
The apparatus of Japanese patent JP10158820, owned by Japanese company—ULVAC JAPAN, can be utilized to purify photoelectric materials, such as N, N′-Bisphenyl-N,N′-bis(3-methylphenyl)-benzidine (TPD). The design aims at improving heating evenness and rate by using noble gases as heat carriers. This process is usually not applied to the purification of the chemicals with low vapor pressure, such as CuPc. Since products are easily contaminated by flowing residues, high vacuum environment cannot be realized. In addition, U.S. Pat. No. 5,377,429, owned by American company—Micron Semiconductor, disclosed a sublimation device to purify the organic metal chemicals employed in the semiconductor industry, such as tetrakis-dimethyl-amino titanium[Ti(N(CH3)2)4] (abbreviated as TDMAT). The unique features of the design are: vaporization and condensation taking place in the same vertical vessel. Raw materials located at the bottom of the vessel are mixed with ceramic beads which act as heat carriers. The sublimation vessel consisting of a mixing device increases the surface area for heat conduction. During the purification process, vapor rises and then condenses on the upper part of the vessel wall, and products can be scratched off after sublimation. However, the raw materials are likely to be spattered, thus causing contamination on products during the mixing process, and products thereof are also difficult to collect. Japanese patent JP200093701, owned by Japanese company—Nippon Steel Chemical Group, outlined an apparatus with separate vaporization and condensation devices. Temperatures thereof are individually controlled by induction heating to purify photoelectric materials, such as Alq3. However, such process cannot apply to mass production due to its poor heating efficiency and incapability to reach the required sublimation temperature (500° C.). U.S. Pat. No. 4,407,488, owned by German company—Leybold-Heraeus GmbH, did not point out what types of materials can be purified by the apparatus. The disclosed sublimation system consists of multiple groups of vaporization plates. Under a vacuum environment, heat is absorbed by plate edges and distributed on plate surfaces to heat and vaporize thin layers of materials on the plate surfaces. This particular heating process is likely to produce uneven temperature profile on plate surfaces, thus making the purity of products hard to be improved.